In the Hewlett-Packard Journal, February 1987, pages 26 and 27, there is described an optical head which, in a rear portion thereof, is formed with photoelectric converter circuitry outputting an electric signal, for example, based upon an incoming light signal. A front portion of this head is provided with an adapter body which constitutes a means for connecting a fiber optical light guide to the photoelectric device. The optical coupling between the photoelectric circuit and the fiber optics serving as an input, includes a socket at the front part of the optical head which receives a light guide plug at the end of the light guide which can be, as noted, a sheathed optical fiber or bundle of optical fibers.
In the conventional optical head described in this publication, detrimental reflections on inner parts of the head are suppressed, inter alia, by a light absorbing coating on the inner end of the adapter body and on the aperture diaphragm formed on the front side of the plug which surrounds the end of the light guide.
This apparatus, therefore, requires special plugs whose front side, like the rear side of the adapter body, must be formed with the light absorbing coating. These coatings are exposed upon withdrawal of the plug or dismounting of the adapter body, so that the coatings are subject to wear and damage.
Furthermore, the light guide must be adjusted with high precision in the plug since the end of the plug also forms the apertured diaphragm.